Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
18 results
Search Results
Item Enhanced thermoelectric performance of bulk tin telluride: Synergistic effect of calcium and indium co-doping(Elsevier Ltd, 2018) Bhat, D.K.; Shenoy, S.SnTe based materials are considered recently as a lead-free replacement of the well-known PbTe based thermoelectric (TE) materials in addressing the energy crisis worldwide. Herein we report both experimental and theoretical study on the effect of co-doping of calcium and indium on electronic structure and TE properties of SnTe. We show that the resonant levels introduced by indium and band gap opening caused by calcium, valence band convergence induced by both calcium and indium, synergistically increases the Seebeck coefficient for a wide range of temperatures. The co-doped SnTe with a high ZT of ?1.65 at 840 K and record high power factor of ?47 ?Wcm?1K?2 for SnTe based materials make it a promising material for TE applications. © 2018 Elsevier LtdItem Electronic structure engineering of tin telluride through co-doping of bismuth and indium for high performance thermoelectrics: A synergistic effect leading to a record high room temperature ZT in tin telluride(Royal Society of Chemistry, 2019) Shenoy, U.S.; Bhat, D.K.The ever increasing demand for alternative clean energy sources has led to intense research towards the optimization of thermoelectric performance of known systems. In this work, we engineer the electronic structure of SnTe by co-doping it with Bi and In. The co-doping not only results in the formation of two different resonance states and a reduced valence band offset, as in the case of previously reported co-doped SnTe, but also leads to opening of the band gap, which otherwise was closed in the case of Bi and In doped SnTe configurations, leading to suppression of bipolar diffusion. The synergistic action of all these effects leads to an increased Seebeck co-efficient throughout the temperature range and a ZTmax of ?1.32 at 840 K. This strategy of co-doping two different resonant dopants resulted in a record high room temperature ZT of ?0.25 at 300 K for SnTe based materials. This work suggests that appropriate combination of dopants to engineer the electronic structure of a material can lead to unpredictable results. © 2019 The Royal Society of Chemistry.Item Zn: a versatile resonant dopant for SnTe thermoelectrics(Elsevier Ltd, 2019) Bhat, D.K.; Shenoy, U.S.SnTe-based materials have been receiving increasing heed in the field of thermoelectrics (TEs) because of their tunable electronic structure. Until now, only In and Bi are reported to introduce resonance level in SnTe. In this work, for the very first time, we report Zn as a resonant dopant in SnTe using first-principles density functional theory calculations. We show that the resonant states introduced by Zn raises the heavy hole valence sub-band above light hole valence sub-band leading to both record high room temperature Seebeck coefficient (~127 ?VK?1 at 300 K) and figure of merit, ZT (~0.28 at 300 K) for SnTe-based materials. The transport properties calculated using Boltzmann transport equations predicts Zn-doped SnTe to be a promising TE material, further confirmed by experimental ZTmaximum of ~1.49 at 840 K and ZTaverage of ~0.78 with 300 K and 840 K as cold and hot ends, respectively. © 2019 Elsevier LtdItem Bi and Zn co-doped SnTe thermoelectrics: Interplay of resonance levels and heavy hole band dominance leading to enhanced performance and a record high room temperature: ZT(Royal Society of Chemistry, 2020) Shenoy, U.S.; Bhat, D.K.Lead free SnTe with a tunable electronic structure has become the front runner in eco-friendly thermoelectrics. Herein, we show through first-principles density functional theory calculations that Bi and Zn doping introduces a resonance level in SnTe. The dominance of the heavy hole valence band at room temperature in Bi-Zn co-doped SnTe leads to a record high room temperature ZT of ?0.3 (at 300 K) for SnTe based materials. The increase in the Seebeck coefficient value due to the interaction between the resonance states and formation of the nanoprecipitates leading to an appreciably low lattice thermal conductivity of 0.68 W m-1 K-1 results in a peak ZT of ?1.6 at 840 K. A record high ZTaverage of ?0.86 with 300 K and 840 K as cold and hot ends, respectively, makes Bi-Zn co-doped SnTe a potential material for thermoelectric applications. This strategy of using two resonant dopants, to not only improve the room temperature ZT but also high temperature values, can very well be extended to other systems. This journal is © The Royal Society of Chemistry.Item SnTe thermoelectrics: Dual step approach for enhanced performance(Elsevier Ltd, 2020) Bhat, D.K.; Shenoy, U.S.Doping of SnTe to achieve desirable properties has been a wide spread approach in the recent past to enhance its thermoelectric performance. Herein, we apply a dual approach: Pb doping for reduction of thermal conductivity and Zn doping for improving the power factor. The theoretical prediction of enhanced Seebeck due to increase in the band gap, introduction of the resonance levels by Zn and dominance of the heavy hole valence band, is realized experimentally as improved power factor throughout the temperature range. The accompanying reduction in the thermal conductivity by co-doping Pb and Zn leads to a record high room temperature figure of merit, ZT of 0.35 (@ 300K) and ZT of 1.66 at 840 K. The ZTaverage of ?0.9 with 300 K as cold end and 840 K as hot end sets a new record for SnTe based materials. © 2020 Elsevier B.V.Item Complementary effect of co-doping aliovalent elements Bi and Sb in self-compensated SnTe-based thermoelectric materials(Royal Society of Chemistry, 2021) Kihoi, S.K.; Shenoy, U.S.; Bhat, D.K.; Lee, H.S.Research on Pb-free thermoelectric materials as a potential eco-friendly and solid-state source of energy has continuously advanced over time, with SnTe-based materials having shown utmost promising properties owing to their tunable electronic structure and scalable thermal conductivity. In this study, we self-compensate Sn to reduce inherent Sn vacancies, and further tune the carrier concentration by doping with Bi. Sb is further alloyed to incorporate nanostructures that significantly reduce the thermal conductivity. Multiple aliovalent dopants result in a continually decreased carrier concentration and subsequent significantly decreased electrical conductivity. The Seebeck values are seen to increase with temperature, where a maximum value of ?171 ?V K?1is reported with a maximum power factor of ?22.7 ?W cm?1K?2. We show through first principles DFT calculations the synergistic effect of Bi and Sb to introduce resonance states and an additional valence band convergence effect with increasing Sb that contribute to improved electronic properties. A decreased phonon frequency with co-doping is also reported. A maximumZTof ?0.8 at 823 K is reported in the Sn0.90Bi0.03Sb0.10Te composition, showing good potential in Sb co-doped SnTe-based materials. © The Royal Society of Chemistry 2021.Item Electronic structure modulation of Pb0.6Sn0.4Te via zinc doping and its effect on the thermoelectric properties(Elsevier Ltd, 2021) Shenoy, U.S.; Bhat, D.K.Striking a balance between the high performance and detrimental environmental toxicity of PbTe materials in thermoelectrics (TE) has become a necessity in the current situation. In this context, improving the performance of materials with lower lead content to the level of PbTe is crucial. Herein, we engineer the electronic structure of Pb0.6Sn0.4Te, a well-known TCI but a poor TE material by doping Zn. The first principles calculation reveal that Zn doping introduces multiple electronic valleys while simultaneously opening the band gap of Pb0.6Sn0.4Te. Higher power factor with lower thermal conductivity is predicted by the transport property calculations in the doped material. The resonance level introduced along with features of hyper-convergence of the valence bands leads to improved Seebeck co-efficient throughout the studied temperature range. An experimental figure of merit, ZT of ~1.57 at 840 K promises us a TE material applicable for a broad temperature range for future energy applications. © 2021 Elsevier B.V.Item Vanadium: A Protean Dopant in SnTe for Augmenting Its Thermoelectric Performance(American Chemical Society, 2021) Shenoy, U.S.; Bhat, D.K.In this work, a second n-type resonant dopant in the form of vanadium is introduced in the SnTe thermoelectrics family. The electronic structure simulated using density functional theory calculations revealed that V not only opens the band gap but also causes convergence of both valence and conduction sub-bands. Apart from introducing the resonance levels at the Fermi energy, the unique trait exhibited is the Rashba splitting of the conduction band to introduce multiple valleys. The advantage is the proximity of these features to the Fermi level, which eliminates the need for a co-dopant to harness the benefits. The Boltzmann transport calculations predicted promising transport properties, which showed the dual nature of vanadium, being capable of acting as a p-type as well as an n-type dopant in SnTe with corresponding maximum ZT values of 1.66 and 1.31, respectively, at 800 K, thus making it a highly potential high-performance thermoelectric candidate for future experimental studies. © 2021 American Chemical SocietyItem Optimized Mn and Bi co-doping in SnTe based thermoelectric material: A case of band engineering and density of states tuning(Chinese Society of Metals, 2021) Kihoi, S.K.; Kahiu, J.N.; Kim, H.; Shenoy, U.S.; Bhat, D.K.; Yi, S.; Lee, H.S.Tin telluride (SnTe) overwhelmingly continues to be studied owing to its promising thermoelectric properties, tunable electronic structure, and its potential as an alternate to toxic lead telluride (PbTe) based materials. In this research, we engineer the electronic properties of SnTe by co-doping Mn and Bi below their individual solubility limit. The First principles density functional theory studies reveal that both Bi and Mn introduce resonance states, thereby increasing the density of states near the Fermi level leading to enhanced Seebeck coefficient. This unique combination of using two resonant dopants to introduce flatter bands is effective in achieving higher performance at lower temperatures manifesting into a large Seebeck value of ?91 ?V/K at room temperature in the present case. Both elements optimally co-doped results in a very high power factor value of ?24.3 ?W/cmK2 at 773 K when compared to other high performance SnTe based materials. A zT of ?0.93 at 773 K is achieved by tuning the proportion of the co-dopants Mn and Bi in SnTe. The hardness value of pristine SnTe was also seen to increase after doping. As a result, synergistic optimized doping proves to be a suitable means for obtaining thermoelectric materials of superior characteristics without the need for heavy doping. © 2021Item Improving the: ZT of SnTe using electronic structure engineering: Unusual behavior of Bi dopant in the presence of Pb as a co-dopant(Royal Society of Chemistry, 2021) Shenoy, U.S.; Bhat, D.K.Electronic structure engineering of SnTe by doping various elements to improve its figure of merit has been the most promising approach recently sought after. Pb doped in SnTe is well known to decrease the thermal conductivity but fails to beneficially tune its electronic properties. Herein, we co-dope Bi in SnTe doped with Pb, to improve the power factor of the material. Bi in the presence of Pb exhibits unusual features not shown in the case of Bi doped SnTe. The synergistic action leads to an increase in the band gap and valence band convergence. Bi also introduces resonance states just below the conduction band edge and causes conduction band convergence. An enhanced power factor due to modification of the electronic structure combined with reduced thermal conductivity translates into an enhanced figure of merit of up to ?1.58 at 800 K as predicted using Boltzmann transport calculations, making it a potential thermoelectric material worthy of further study. This journal is © The Royal Society of Chemistry.